Plant invasion in Mediterranean Europe: current hotspots and future scenarios

The Mediterranean Basin has historically been subject to alien plant invasions that threaten its unique biodiversity. This seasonally dry and densely populated region is undergoing severe climatic and socioeconomic changes, and it is unclear whether these changes will worsen or mitigate plant invasions. Predictions are often biased, as species may not be in equilibrium in the invaded environment, depending on their invasion stage and ecological characteristics. To address future predictions uncertainty, we identified invasion hotspots across multiple biased modelling scenarios and ecological characteristics of successful invaders. We selected 92 alien plant species widespread in Mediterranean Europe and compiled data on their distribution in the Mediterranean and worldwide. We combined these data with environmental and propagule pressure variables to model global and regional species niches, and map their current and future habitat suitability. We identified invasion hotspots, examined their potential future shifts, and compared the results of different modelling strategies. Finally, we generalised our findings by using linear models to determine the traits and biogeographic features of invaders most likely to benefit from global change. Currently, invasion hotspots are found near ports and coastlines throughout Mediterranean Europe. However, many species occupy only a small portion of the environmental conditions to which they are preadapted, suggesting that their invasion is still an ongoing process. Future conditions will lead to declines in many currently widespread aliens, which will tend to move to higher elevations and latitudes. Our trait models indicate that future climates will generally favour species with conservative ecological strategies that can cope with reduced water availability, such as those with short stature and low specific leaf area. Taken together, our results suggest that in future environments, these conservative aliens will move farther from the introduction areas and upslope, threatening mountain ecosystems that have been spared from invasions so far

Shedding light on typical species : implications for habitat monitoring

Habitat monitoring in Europe is regulated by Article 17 of the Habitats Directive, which suggests the use of typical species to assess habitat conservation status. Yet, the Directive uses the term “typical” species but does not provide a definition, either for its use in reporting or for its use in impact assessments. To address the issue, an online workshop was organized by the Italian Society for Vegetation Science (SISV) to shed light on the diversity of perspectives regarding the different concepts of typical species, and to discuss the possible implications for habitat monitoring. To this aim, we inquired 73 people with a very different degree of expertise in the field of vegetation science by means of a tailored survey composed of six questions. We analysed the data using Pearson's Chi-squared test to verify that the answers diverged from a random distribution and checked the effect of the degree of experience of the surveyees on the results. We found that most of the surveyees agreed on the use of the phytosociological method for habitat monitoring and of the diagnostic and characteristic species to evaluate the structural and functional conservation status of habitats. With this contribution, we shed light on the meaning of “typical” species in the context of habitat monitoring

Microdon devius

Immature stages of Microdon devius Third instar larva Figs 7–9 Body width = 7.2 ± 0.6 mm; body length = 9.4 ± 0.9 mm (n = 10). Dorsal reticulation. Dorsal reticulation extended over the whole dorsal body surface. Each process resembling a sea anemone, being divided into a smooth, columnar trunk topped by a brush composed by 20–30 long, flexible filaments (Fig. 7F). Posterior spiracular tubercle. Longer than wide, subquadrate in dorsal view, concave medially, bulged sub–basally; distance between spiracular holes 1.8 times as long as their diameter (Figs 8E, F). The base of posterior spiracular tubercle encircled by a smooth cuticular crown (Figs 8E, F). Spiracular plates flattened to slightly concave, of variable shape, separated by a broad and deep midsagittal cleft. Marginal band. Processes on the marginal band apparently without basal articulated joints (Figs 9E, F). Processes on the marginal band of three types: type one long and single, apically fringed; type two short and bifurcate, apically 2–lobed; type three composed by two type one flanking a cluster of three spiniform setae (Figs 9E, F). Puparium Figs 10, 11 Body width = 7.3 ± 0.4 mm; body length = 9.7 ± 0.5 mm (n = 10). Anterior spiracular tubercles. Length of each tubercle 2.25 times as long as wide and strongly curved (Fig. 11F), subcylindrical, slender, somewhat pointed at the apex, entirely furrowed by about 180 respiratory fissures (Figs 10E, F). Each fissure laying on a small papilla (Fig. 10F).Published as part of Scarparo, Giulia, Wolton, Robert, Molfini, Marco, Pinna, Luigi Cao & Ulio, Andrea Di Gi-, 2020, Comparative morphology of myrmecophilous immature stages of European Microdon species (Diptera: Syrphidae): updated identification key and new diagnostic characters, pp. 348-370 in Zootaxa 4789 (2) on pages 360-362, DOI: 10.11646/zootaxa.4789.2.2, http://zenodo.org/record/399083

Microdon myrmicae Schonrogge

Immature stages of Microdon myrmicae Egg Figs 1, 11 Width = 587.4 ± 36.61 µm; length = 1.08 ± 0.03 mm (n = 10). First instar larva Figs 2−6, 11, Supplementary Material 1 Body width = 679.5 ± 55.42 µm; body length = 0.996 ± 0.08 mm (n = 10). Body features. Body with regularly rounded sides. Four longitudinal grooves present dorsally (Fig. 2A) dividing dorsal body surface into five main longitudinal fields: one medial, two lateral and two external fields. Medial field partially divided into two halves by a longitudinal, medial line. Dorsal surface with regularly spaced “flower-like” sensilla (Figs 3A, E): medial field with two longitudinal rows of nine sensilla; each lateral field with 13 sensilla arranged in two rows (seven along lateral groove and six along medial groove); each external field with one row of 10 sensilla. Each sensillum (Fig. 3E) composed of a cylindrical base, with many imbricate, thick sculpticels, apically with a medial flower-like structure with a variable number (5–10) of long lobes, pointed at tip, encircling a medial dome. Ventral surface covered medially by pointed microsculpture, finely pilose on sides. Ventral flower-like sensilla (Figs 3C, G) similar to dorsal ones except for flat, soft, unsculptured base and flat, thin, distinctly pointed lobes. Pseudocephalon. Two pairs of sensorial organs on dorsal surface of pseudocephalon (Figs 4E, G), one anterior (Fig. 4E) and one posterior (Fig. 4G), each composed of clusters of four short and one long trichoid sensilla emerging from bulbous, hollow base. Posterior spiracular tubercle. Impair respiratory structure, elongated in shape; surface of spiracular tubercle with peculiar microsculpture, completely covered by imbricate, sclerotised scales with an irregularly indented apex (Fig. 5A). Apex of tubercle with two circular smooth plates, slightly convex (Fig. 5C). Marginal band. Distinctly long fringe, length of processes regularly varying, showing eight waves on each side (Figs 2A, E, 6A, C, E). Each individual process composed of an elongate stem and an apical fringed brush (Figs 6A, C, E); the stem showing two very different surfaces: dorsal surface apparently articulated with 4–5 imbricated joints, the distal one fringed apically (Figs 6A, E); ventral surface completely smooth (Fig. 6C). Third instar larva Figs 7−9, 11 Body width = 4.5 ± 0.7 mm; body length = 6.1 ± 0.8 mm (n = 10). Dorsal reticulation. Dorsal reticulation reduced to a narrow, lateral belt around the perimeter of abdomen (Figs 7A, B). Each reticulation process showing sub circular groups of 5–9 umbrella-like structures with a flattened, circular apex (Figs 7A, B). Posterior spiracular tubercle. Dome shaped with two round holes spaced 1.2 times as long as their diameter; apex divided into two halves (Figs 8A, B) by a narrow furrow showing irregular plates. Marginal band. Processes on the marginal band short and thick, set close to one another, parallel, radially projecting, with suboval basal “joints”, not imbricated, the last one produced into a flat medial brush. Processes on the marginal band of three types (Figs 9A, B): type one basally 4–jointed and apically single and flat, with medial brush 2–lobed; type two basally 3–jointed and apically bifurcate, with medial brush 1–lobed; type three basally 3–jointed and apically produced into a group of three spiniform setae. Type one and type two regularly alternating in sequence, type three irregularly present between two type one processes. Puparium Figs 10, 11 Body width = 6.1 ± 0.5 mm; body length = 7.9 ± 0.7 mm (n = 10). Anterior spiracular tubercles. Length of each tubercle about 1.4 times as long as wide, conical, tapering at the apex (Fig. 10A, B), smooth at the base, with the apex furrowed by about 150 respiratory fissures (Figs 10A); each fissure laying on a small papilla (Fig. 10B).Published as part of Scarparo, Giulia, Wolton, Robert, Molfini, Marco, Pinna, Luigi Cao & Ulio, Andrea Di Gi-, 2020, Comparative morphology of myrmecophilous immature stages of European Microdon species (Diptera: Syrphidae): updated identification key and new diagnostic characters, pp. 348-370 in Zootaxa 4789 (2) on pages 354-357, DOI: 10.11646/zootaxa.4789.2.2, http://zenodo.org/record/399083

Invasion success on European coastal dunes

Many invasive plants are threatening the already highly vulnerable habitats of coastal dunes in Europe. Setting priority target species to control is mandatory for an effective planning of invasion management strategies at European level. This can be possible after identifying the species that currently have greater invasion success, in consideration of their ecological traits and origin. We quantified the three main components of invasion success for the extra-European alien plants found on European coastal dunes: local abundance, regional distribution and niche breadth, and related them to their life forms and origins. We found that life form was a better predictor of invasion success. In particular, geophytes and therophytes were the species with the greatest invasion success. Quite surprisingly, alien plants from Africa appeared as the group with slightly higher mean invasion success although this result was no statistically significant. We also highlighted the species deserving special attention. Among these, Xanthium orientale, Erigeron canadensis and Oenothera gr. biennis showed the widest levels of niche breadth and regional distribution, and had overall the greatest invasion success, but other species also had high levels in one of the three components of invasion success

Microdon Meigen 1803

Keys to immature stages of the European species of Microdon First instar larvae 1 Body about 1.5 times as long as wide; posterior spiracular tubercle long (more than 1.5 times as long as wide at base); marginal band elongate, showing eight waves on each side...................................... M. myrmicae / M. mutabilis - Body about two times as long as wide; posterior spiracular tubercle very short (wider than long at base); marginal band short, showing 10 waves on each side................................................................... M. analis Puparia 1 Most of the dorsal surface of puparium smooth and bare, with reticulation reduced to a narrow, lateral belt.............. 2 - Dorsal surface of puparium completely covered by a dorsal reticulation.......................................... 3 2 Anterior spiracular tubercles conical, tapering at apex; anterior spiracular tubercles about 1.4 times as long as wide at base; each reticulation process composed of groups of umbrella-like structures................................... M. myrmicae - Anterior spiracular tubercles dome-shaped, blunt at apex; anterior spiracular tubercles about 0.8 times as long as wide at base; each reticulation process composed of stringy, extended projections.................................... M. mutabilis 3 Meshes of the dorsal reticulation no broader than the basal diameter of the posterior spiracular tubercle; posterior spiracular tubercle wider than long; anterior spiracular tubercles straight................................................. 4 - Meshes of the dorsal reticulation two times as broad as the basal diameter of the posterior spiracular tubercle; posterior spiracular tubercle longer than wide; anterior spilacural tubercles laterally curved................................. M. devius 4 Anterior spiracular tubercles equal or more than two times as long as wide....................................... 5 - Anterior spiracular tubercles one time only as long as wide, or shorter than wide.............................. M. miki 5 Anterior spiracular tubercles nearly cylindrical, about three times as long as wide; posterior spiracular tubercle light-brown contrasting with the reddish-brown apical spiracular plates.............................................. M. analis - Anterior spiracular tubercles clearly conical, about two times as long as wide; posterior spiracular tubercle uniformly reddishbrown....................................................................................... M. majorPublished as part of Scarparo, Giulia, Wolton, Robert, Molfini, Marco, Pinna, Luigi Cao & Ulio, Andrea Di Gi-, 2020, Comparative morphology of myrmecophilous immature stages of European Microdon species (Diptera: Syrphidae): updated identification key and new diagnostic characters, pp. 348-370 in Zootaxa 4789 (2) on pages 364-365, DOI: 10.11646/zootaxa.4789.2.2, http://zenodo.org/record/399083

Exploring temporal trends of plant invasion in mediterranean coastal dunes

© 2021 by the authors.Alien plants represent a significant threat to species diversity and composition in natural habitats. Nevertheless, little is known about the dynamic of the invasion process and how its effects on native species change over time. In this study, we explored vegetation changes that occurred in invaded coastal dune habitats over the last 10–15 years (2005–2020), particularly addressing impacts on alien and diagnostic species. To monitor temporal trends, we used data resulting from a revisitation study. After detecting overall changes in alien species occurrence and cover over time, 127 total plots were grouped into plots experiencing colonization, loss, or persistence of alien species. For these three categories, we compared historical and resurveyed plots to quantify changes in native species composition (using the Jaccard dissimilarity index) and to measure variations in diagnostic species cover. The number of alien species doubled over time (from 6 to 12) and two species, Yucca gloriosa and Agave americana, strongly increased their cover (+5.3% and +11.4%, respectively). Furthermore, plots newly invaded appeared to record the greatest changes in both native and diagnostic species. Our results suggest the need for regular monitoring actions to better understand invasion processes over time and to implement effective management strategies in invaded coastal dune habitats

Exploring Temporal Trends of Plant Invasion in Mediterranean Coastal Dunes

Alien plants represent a significant threat to species diversity and composition in natural habitats. Nevertheless, little is known about the dynamic of the invasion process and how its effects on native species change over time. In this study, we explored vegetation changes that occurred in invaded coastal dune habitats over the last 10–15 years (2005–2020), particularly addressing impacts on alien and diagnostic species. To monitor temporal trends, we used data resulting from a revisitation study. After detecting overall changes in alien species occurrence and cover over time, 127 total plots were grouped into plots experiencing colonization, loss, or persistence of alien species. For these three categories, we compared historical and resurveyed plots to quantify changes in native species composition (using the Jaccard dissimilarity index) and to measure variations in diagnostic species cover. The number of alien species doubled over time (from 6 to 12) and two species, Yucca gloriosa and Agave americana, strongly increased their cover (+5.3% and +11.4%, respectively). Furthermore, plots newly invaded appeared to record the greatest changes in both native and diagnostic species. Our results suggest the need for regular monitoring actions to better understand invasion processes over time and to implement effective management strategies in invaded coastal dune habitats

Exploring Temporal Trends of Plant Invasion in Mediterranean Coastal Dunes

Alien plants represent a significant threat to species diversity and composition in natural habitats. Nevertheless, little is known about the dynamic of the invasion process and how its effects on native species change over time. In this study, we explored vegetation changes that occurred in invaded coastal dune habitats over the last 10–15 years (2005–2020), particularly addressing impacts on alien and diagnostic species. To monitor temporal trends, we used data resulting from a revisitation study. After detecting overall changes in alien species occurrence and cover over time, 127 total plots were grouped into plots experiencing colonization, loss, or persistence of alien species. For these three categories, we compared historical and resurveyed plots to quantify changes in native species composition (using the Jaccard dissimilarity index) and to measure variations in diagnostic species cover. The number of alien species doubled over time (from 6 to 12) and two species, Yucca gloriosa and Agave americana, strongly increased their cover (+5.3% and +11.4%, respectively). Furthermore, plots newly invaded appeared to record the greatest changes in both native and diagnostic species. Our results suggest the need for regular monitoring actions to better understand invasion processes over time and to implement effective management strategies in invaded coastal dune habitats